Abhishek kumAr is Senior Engineer, SBP (Strategic

Business Planning) at the International Centre for

Automotive Technology (ICAT), based in Manesar, India

VArun AggArwAl is Senior Engineer, VED (Vehicle

Evaluation Department) at the International Centre for

Automotive Technology (ICAT), based in Manesar, India

The International Centre for Automotive Technology (iCAT) is the first organisation in Asia to have procured

the Dynatest 995 Tire Traction Tester (TTT) – an equipment used to measure skid and slip friction characteristics

on paved surfaces. The equipment comprises of a fully-instrumented tow vehicle and a test trailer

that uses a Dynatest two-axis force transducer. We bring you exclusive details of the machine that is likely

to change the way tyre manufacturers tested their products in India.

Tire TracTion TesTer Icat Offers sOlutIOn tO Measure skId, slIp

AuTHorS

❶ Hydroplaning

Accidents on roads are accounting for over 1.3 million lives annually. Injury and deaths due to road traffic crashes are a major public health problem in develop-ing countries. Approximately 90 % of these deaths occur in low and middle-income countries. Estimates suggest road traffic injuries would rise from their cur-rent position as the ninth leading cause of deaths, to become the fifth leading cause of deaths by 2030 [1].

The global economic cost of multi-vehicle crash was estimated at $ 518 bn per year in 2003 with $ 100 bn of that being accounted for by developing coun-tries [2].

One of the most common causes of road accidents is the loss of traction avail-able at tyre-road interaction during risk manoeuvres, such as braking, cornering

or lane changes. Safety features like Anti-lock Braking System (ABS) and Electronic Stability Program (ESP), which are availa-ble in most modern cars today, help main-tain traction at tyre-pavement contact, at an optimum level available in these conditions.

Traction or grip of a tyre is its road holding capability in various conditions of manoeuvre, both in dry and wet roads. The traction (grip) available depends on both tyre (tread compound & pattern) and road surface type (dry & wet).

Tread patterns that are good for wet traction have deep grooves that keep water out from underneath the tyres. These grooves keep a film of water from forming under the tyres, while you drive, as water trapped between the tyres and the road causes hydroplaning, 1.

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Hydroplaning causes severe loss of traction capability of tyre, which sub-sequently could affect vehicle control and may result in serious traffic accidents [3, 4]. Hydroplaning of tyres is a common situation on wet roads and during rainy seasons. Wet roads offer lower friction values, resulting in increased braking dis-tance. This too could lead to accidents.

A vast majority of weather-related crashes happen on wet pavements and during rainfall. In the United States, 75 % of these accidents happen on wet pave-ments and 47 % during rainfall [5]. A study conducted in New Delhi estimated that 16.7 % of the crashes occurred on wet days [4]. Proportion of accidents on wet days were generally reported to be double than on dry days [6].

regulAtions & meAsurements

While making a purchase decision, con-sumers generally don’t consider a tyre’s traction capability. In order to equip con-sumers with information regarding the wet grip of tyres, along with tyre-road noise and rolling resistance, the United Nations Economic Commission for Europe (UNECE) came up with a proposal for tyre labelling.

Subsequently, Regulation EC No. 1222/2009 was introduced for labelling

wet grip rating values, which will be effective for all new tyres sold in the Euro-pean Market starting November 2012, 2. Wet grip measurement of passenger car tyres is done in accordance with UNECE R117 and ISO 23671 regulations, through the vehicle and trailer methods.

Wet grip index (W) means the ratio between the performance of the candidate tyre (representative of the type, which is submitted for approval in accordance with this regulation) and the performance of the Standard Reference Test Tyre (SRTT).

With this, iCAT expects to help tyre manufacturers evaluate their tyre and readiness for future regulations.

tire trAction tester: the Product

The Tire Traction Tester (TTT) procured from Dynatest Inc. is used to evaluate wet grip index of tyres as per UNECE R117 and ISO 23671 regulations. As a pavement measurement device, the TTT meets all the requirements of ASTM-E274 (specification for skid resistance using a full scale tyre) as well as ASTM-F408 (standard test method for tyres for wet traction in straight ahead braking, using a towed trailer).

The product consists of a fully instru-mented tow vehicle and test trailer equipped with a two axis force transducer.

The force transducer provides dynamic vertical load and horizontal traction force measurement. Using these values, average locked wheel (skid) and peak incipient (slip) friction of tyre on paved surface is measured. The product can also be used to evaluate dry or self-wetted skid and slip characteristics of tyres at operational speeds of 30 to 110 km/hr.

Other instruments used by the TTT to produce desired results include, tachome-ter for distance counting (wheel encoder distance pulse counting) and velocity measurement (timer latch counting); a brake system for brake activation and a water system for nozzle activation.

Manufacturer of the product, Dynatest Inc was founded in 1976 in Denmark by a group of engineers and technicians, who combined science, technology and busi-ness into the development and manufac-turing of highly specialised equipment and methodology for pavement engineering.

testing And Processes

UNECE R117 and ISO 23671 regulations require measurement of peak coefficient of friction available at the tyre-pavement contact on a wet surface. The amount of water or water layer thickness is kept between 0.5-1.5 mm with the help of

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a nozzle spraying water at tyre-pavement interactions. These values are measured for tyre fitted on trailer under maximum braking force, using air over hydraulic braking system for a fixed interval of time (0.2 to 0.5 sec). During the measurement, tow-vehicle speed is kept at constant 62 ±2 km/hr as per standard require-ment. A series of tests are conducted with candidate and standard reference test tyres to evaluate wet grip index of the tyre.

references

[1] 2nd global Status report on road Safety, http://www.who.int/violence_injury_prevention/road_safety_status/en/index.html. 2012[2] ”www.searo.who.int”2003 World Health organization. http://www.searo.who.int/LinkFiles/whd04_Documents_un_secretary_general_report_on_orad_traffic_injuries.pdf [3] Cho, J.r., Lee, H.W., Yoo, W.S. ”2006 A wet-road braking distance estimate utilizing the Hydroplaning analysis of patterned tire” Int. J. numer. Meth. Engng. 69,1423–1445.[4] Mondal, P., Sharma, nitin., Kumar, A., Vijay, P., Bhangale, u. D., Tyagi, D., (2011). ”Are road

accidents affected by rainfall? A case study from a Large Metropolitan City”. British Journal of Applied Science & Technology 1(2): 16-26.[5] “Weather related Crash Statistics” http://www.ops.fhwa.dot.gov/weather/ q1_roadimpact.htm[6] gothié, M. (2000). “The contribution to road safety of pavement surface characteristics”. Bulletin des Laboratoires des Ponts et Chaussees, (224), 5-12.

2 Tyre Labelling Information

The TTT has been procured from Dynatest Inc., of the uS.

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During the measurement, tow-vehicle speed is kept at constant 62 ±2 km/hr as per standard requirement.

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